1. Field of the Invention
The present invention relates to a method and related communications device for enhancing operation of continuous packet connectivity, and more particularly, to a method and related communications device for enhancing discontinuous packet operation of continuous packet connectivity for a user equipment in a wireless communications system.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. For HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a Continuous Packet Connectivity (CPC) protocol specification, which includes features that, for user equipments (UEs) in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP.
For an HSDPA UE, physical channels include a high speed physical downlink shared channel (HS-PDSCH), for transferring payload data, and a high speed physical control channel (HS-DPCCH) for uploading an acknowledgement/negative acknowledgement (ACK/NACK) and a channel quality identifier (CQI). As for the media access control (MAC) layer of the HSDPA UE, a MAC-hs entity utilizes a transport channel of High Speed Downlink Shared Channel (HS-DSCH) for receiving data from the physical layer. In addition, a shared control channel for HS-DSCH (HS-SCCH) is used as a physical downlink channel, responsible for transmission of control signals corresponding to HS-DSCH, such as demodulation information.
For an HSUPA UE, physical channels includes two uplink channels: an enhanced dedicated transport channel dedicated physical data channel (E-DPDCH), for transferring payload data, and an E-DCH dedicated physical control channel (E-DPCCH) for transmission of control signals, such as retransmission numbers. Furthermore, a bundle of downlink physical channels are employed in the HSUPA system and used for transmitting control signals associated with grants, ACKs and etc. The downlink physical channels include E-DCH relative grant channel (E-RGCH), E-DCH absolute grant channel (E-AGCH), E-DCH HARQ acknowledgement indicator channel (E-HICH) and fractional dedicated physical channel (F-DPCH). As for the MAC layer of the HSUPA UE, a MAC-e/es entity utilizes a transport channel of enhanced dedicated transport channel (E-DCH) for transmitting MAC packet data to the physical layer with supporting a transmission time interval (TTI) of 10 milliseconds (ms) or 2 ms.
For CELL_DCH state, CPC operation defines an active state and an inactive state. For any data channels (ex. E-DCH), the active state represents that there are data packets transmitted on the data channels. For any control channels (ex. HS-DPCCH), the active state represents that there are data packets transmitted on the data channels corresponding to the control channels, such as HS-PDSCH corresponding to HS-DPCCH. On the contrary, for any data channels, the inactive state represents that there are no data packets transmitted on the data channels. For any control channels, the inactive state represents that there are no data packets transmitted on the data channels corresponding to the control channels.
According to the CPC protocol specification, discontinuous uplink transmission (uplink DTX) is a mechanism where control signals are transmitted on the uplink control channels according to defined discontinuous patterns during the inactive state of corresponding uplink data channels in order to maintain signal synchronization and power control loop with less control signaling. The uplink control channels include a normal DPCCH in addition to the abovementioned uplink control channels of HSUPA and HSDPA. The uplink DTX defines two patterns associated with parameters of UE_DTX_cycle—1 and UE_DTX_cycle—2. The former is applied depending on the duration of E-DCH inactivity while the latter adopts a longer transmission cycle and is applied to the inactivity of any uplink control channels. In each UE_DTX_cycle_pattern, the UE shall not transmit data on DPCCH except for a short burst of UE_DPCCH_burst_subframes. For example, if the UE_DTX_cycle—1 is set to be four E-DPCCH subframes, the UE transmits a short burst of UE_DPCCH_burst—1 in the first E-DPCCH subframe and stops DPCCH transmission in subsequent three E-DPCCH subframes. In addition, according to an Inactivity_threshold_for_UE_DTX_cycle—2 parameter, the UE can determine whether to transmit a shot burst of UE_DPCCH_burst—2 subframes once every UE_DTX_cycle_2 pattern. UE_DTX_DRX_Offset is used for controlling active time of UE_DTX_cycle—1/2 pattern, allowing different UEs to have uplink transmission phase at different times.
Discontinuous uplink reception (uplink DRX) of CPC is utilized to control the UE to transmit E-DCH in specific time interval and has to be configured with uplink DTX. If there has been no E-DCH transmission for a configurable number of transmission time intervals (ex. the interval of UE_inactivity_Threshold), a radio network controller (RNC) can configure the UE to restrict the start of E-DCH transmission to a MAC_DTX_cycle pattern. UE_DTX_DRX_Offset is also used in uplink DRX, allowing the UEs to have different E-DCH start time.
Discontinuous downlink reception (downlink DRX) of CPC is configured by the RNC and allows the UE to restrict the downlink reception times in order to reduce power consumption. When the downlink DRX is enabled, the UE is not required to receive physical downlink channels except for several specific situations, which refer to 3GPP TSG-RAN WG2 #56 R2-063567. If the UE listens to HS-SCCH with downlink DRX, the UE receives one HS-SCCH subframe according to subframes of a UE_DRX_cycle pattern. For example, if the UE_DRX_cycle pattern is set to be four HS-SCCH subframes, the UE receives one HS-SCCH subframe and rests in the subsequent three HS-SCCH subframes. UE_DTX_DRX_Offset is used for staggering different start time of HS-SCCH reception for the different UEs. Furthermore, Downlink DRX has to be configured with uplink DTX configuration.
As to radio resource control (RRC), the UE and the network, such as the Node-B or a radio network controller (RNC), can configure DTX/DRX operation by exchanging RRC messages and information elements (IEs) that include the abovementioned parameters and modes. According to the RRC protocol specification of 3GPP, a Continuous Packet Connectivity Timing information IE is provided to include a number of timing information parameters (ex. UE_DTX_DRX_Offset) for delaying the start of CPC operation in reconfiguration and offsetting the uplink transmission pattern between different UEs. The timing information can be used to switch off and on the CPC operation and indicate if the current CPC parameters are kept during reconfiguration procedures so that sending full parameter list can be avoid. In addition, a Continuous Packet Connectivity DTX-DRX information IE includes configuration of UE_DTX_cycle—1/2, UE_DPCCH_burst—1/2, Inactivity_threshold_for_UE_DTX_cycle—2, MAC_DTX_cycle and other parameters. The above IEs can be included in RRC CONNECTION SETUP, ACTIVE SET UPDATE, CELL UPDATE CONFIRM or other reconfiguration messages, and can be transmitted to the UE through RRC procedures. On the other hand, the UE stores the DTX/DRX configuration received in the reconfiguration messages into a CPC_DTX_DRX_PARAMS variable.
Furthermore, the UE includes a CPC_DTX_DRX_STATUS variable having two possible values of “TRUE” and “FALSE, which represent the in-use state and the out-of-use state of the DTX/DRX operation, respectively. According to the RRC specification, the UE is required to determine the value for CPC_DTX_DRX_STATUS variable if receiving any reconfiguration messages. Under the CPC_DTX_DRX_STATUS determination, the CPC_DTX_DRX_STATUS variable shall be set to “TRUE” when all of the following conditions are met:                1. the UE is in CELL_DCH state;        2. both HS_DSCH RECEPTION and E_DCH_TRANSMISSION variables are set to “TRUE”;        3. no DCH transport channel is configured;        4. the CPC_DTX_DRX_PARAMS is set;        5. the UE has received a Continuous Packet Connectivity timing information IE from the latest reconfiguration message.        
If any of the above conditions is not met and the CPC_DTX_DRX_STATUS variable is set to be “TRUE”, the UE shall:
1. set the CPC_DTX_DRX_STATUS variable to be “FALSE”;
2. clear the CPC_DTX_DRX_PARAMS variable;
3. stop all related activities of DTX/DRX operation.
Whenever the CPC_DTX_DRX_STATUS variable is set to “TRUE”, the UE shall configure the physical and MAC layers to operate according to the CPC_DTX_DRX_PARAMS variable.
According to the above, the UE determines the value for the CPC_DTX_DRX_STATUS variable only when receiving reconfiguration messages, and the DTX/DRX operation is only applied to the UE in CELL_DCH. If a radio link failure or a radio link control (RLC) unrecoverable error occurs or if transmission of a UE CAPABILITY INFORMATION message fails during DTX/DRX operation, the UE shall perform a cell update procedure to remedy those situations. When initiating the cell update procedure, the UE shall move to CELL_FACH state and select a suitable UMTS radio access (UTRA) cell for submitting a CELL UPDATE message. However, the prior art specification specifies no related actions of DTX/DRX operation under the abovementioned situations. As a result, the UE of the prior art does not re-determine the CPC_DTX_DRX_STATUS variable when moving out of CELL_DCH state. That is, the UE continues applying DTX/DRX operation in CELL_FACH state, which is not applicable for DTX/DRX operation. This may cause severe errors in the physical and MAC layers of the UE.
The radio link failure may occur when the UE is situated in poor signal distributing area, such as a basement or rural area with small coverage. The RLC unrecoverable error is likely to occur due to many causes, such as RLC reset errors or RLC recovery errors. The UE CAPABILITY INFORMATION message is utilized to notify the UTRAN of information of specific UE capability (ex. radio access capability).